Optical lenses, also briefly called lenses, are known whose shape can be altered, consequently altering the focal length. The lens can consist of a jelly-like material and be altered e.g. in outer diameter for changing the focal length. Alternatively, the lens can consist of the liquid drop which, either alone or with the carrier or together with a second liquid, assumes a lens-like bulge, in this manner creating the focal length or, more generally, a lens function. The latter is called “liquid lens” and consists of an optical system which comprises at least the liquid drop and which is optically as highly transparent as possible for a light to be refracted or focused or defocused. This requires for the liquid drop, through which the light at least also penetrates and is refracted, to be also as highly transparent as possible. The liquid drop is a small amount of the liquid of which at least one side has an adjustable bulge with which the refraction can be adjusted.
From KR 10 2008 0 035 252 A, a liquid lens is known which maintains the liquid drop in a cylindrical container, the liquid being in galvanic contact with an electrode and having a conductivity such that the bulge of the liquid can be altered, and thus the lens function controlled, by means of exterior electrical fields applied with reference to the electrode.
From US 2012 0 026 599 A1 , a different liquid lens is known, the liquid drop of which is located in a hole of an intermediate wall of a two-chamber carrier, an additional incompressible liquid, which does not mix with the liquid drop, being filled in on both sides up to exterior walls of a respective first and second chamber with a light inlet or an opposite light outlet, respectively.
The liquid drop in the center forms a corresponding bulge against the additional fluid, creating the lens function in this manner. The intermediate wall has a second hole between the first and the second chamber, in which there is a drop of a ferrofluid which is coupled via the additional incompressible liquid with the liquid drop by volume wise. In this manner, by drawing of the ferrofluid drop in one direction by means of a magnetic field applied from the outside, the liquid drop is drawn in the opposite direction, altering the respective bulges of the liquid drop and correspondingly the focal length with different refraction indices of the liquids.
From US 2009 0 046 195 A1, another liquid lens is known which substantially consists of a liquid drop and an adjacent ferrofluidic liquid which does not mix with the liquid drop, the liquids being arranged between two transparent walls of the carrier. The bulge causing the refraction, which bulge is located between the liquid drop and the ferrofluidic liquid, can be altered by a magnetic field applied on the outside. Here as well as in the examples below, it is a matter of course that the liquids have different refractive indices in order to create a lens function with a focal length.
From US 2002 0 196 558 A1 and US 2005 0 088 754 A9, other embodiments of liquid lenses are known where the liquid drop, which has electric conductivity and is arranged on a carrier, can be shifted and deformed by electrical fields applied on the outside. Thus, the lens function can be altered not only in focal length but also in its spatial position.
WO 2009 123 606 A discloses a variable liquid lens whose shape and, therefore, whose focus is altered by a variable pressure under the lens. The variable pressure is created by a liquid in an enclosing chamber the volume of which can be altered, for instance, by a magnetic plate in combination with an electromagnet.
U.S. Pat. No. 5,074,629 A discloses a different type of variable liquid lens where for instance a silicon layer has a cavity filled with a transparent liquid and equipped with a transparent cover, where a temperature change causes the cover to bulge and adjusts the focus. Such liquid lenses can be manufactured particularly in miniature size.
US 2007 279 757 A1 discloses a liquid lens created by an electrically conductive and an electrically non-conductive liquid which are adjacent to each other and can be altered in shape by an electrical field. The device in particular has a heating element so that the liquid lens can also be used at low temperatures and without any particular influence of the ambient temperature.
US 2008 0198 473 A1 discloses a liquid lens formed by a first and a second liquid which together form a parting layer, the second liquid being a ferrofluid. By a magnetic field applied on the outside, the shape of the ferrofluid, and in particular the parting layer between the first and the second liquid, become concave or convex as in a lens, creating a specific focus. For avoiding or reducing, in case of a strong change in focus, an optical distortion at an edge of the parting layer adjacent to the enclosure wall, the enclosure wall is embodied in accordance with the disclosure.
Difficulties resulting from many of the embodiments of a liquid lens and in practical long-term use are evaporation of the liquid drop and safely keeping the drop on the carrier. Also, deformation of the liquid drop due to electrostatic attraction or repulsion can be problematic under certain circumstances in terms of a desired lens function, since attraction or repulsion are non-linear with the displacement path. Also, for electrostatic attraction of the liquid drop in one direction, often a high voltage is necessary which is problematic in small electronic circuits or has disadvantages in terms of energy efficiency. Since the liquid drop must be conductive, not all liquids are suitable which would be suitable in terms of light transparency and refractive index.